This invention relates to the field of optical energy beam signal phase correction by a controllable selective refraction.
It is desirable to alter phase relationships across the spatial extent of an optical energy beam for the lasers contemplated in space weapons as part of the strategic defense initiative (SDI) program, for scientific laser applications, and in many optical energy transfer and signal processing applications. A need for phase alteration can arise from a need to reshape such an energy beam, a need to assure effective mode selection in a laser device, or the need to pack the laser beam and deliver a maximum amount of optical energy to a small, far field location as would be desired in a laser weapon device.
For laser weapons the use of chemical lasers, that is, lasers achieving stimulated emission with the energy derived from chemical reactants and produce optical energy in the infrared or far-infrared spectral region are most practical. In such lasers a gain generating apparatus, possibly in the form of a cylindrical body is placed within an optical resonance cavity that includes a pair of reflective devices. The gain generator in such a cylindrical chemical laser provides an annular shaped elongated field of high temperature gain media which is optically aligned with the reflective devices of the resonant cavity to comprise the functional laser. Lasers of this type have the notable advantages of providing large energy output, receiving energy input from conveniently portable sources, e.g., flasks of high-pressure gases, and being of relatively small overall weight per joule of delivered optical energy. In space use, such lasers encounter the desired total vacuum operating conditions; the earth testing of such lasers, of course, involves the considerable complexity of simulating vacuum operating conditions.
Inevitable imperfections or variations in the high temperature gain medium of such a chemical laser--imperfections resulting from reactant feed non-uniformities and other practical considerations, usually result in optical wavefront phase distortions in the energy delivered from their resonant cavity. These phase distortions can be observed by examination of the optical energy annulus emanating from the periphery of a cylindrical gain generator device. Such energy usually has an azimuthally varying cosine phase distortion pattern wherein the wavefront is found to contain a phase non-uniformity when observed in a circular path around the energy annulus. Periodic cosine and higher frequency cosine Fourier components of phase variation around the annular shape of a chemical laser output beam can be attributed to the presence of essentially discrete reaction chambers around the periphery of a gain generator structure in the usual cylindrical arrangement of a chemical laser.
Correction of this phase distortion can be achieved at least partially by selectively increasing optical attention--to provide uniform gain media surrounding the gain generator structure. In view of the limited space, the high gas velocities and large temperature changes involved in such apparatus and the need for the highest possible optical efficiency in a weapon laser device, a more practical arrangement for achieving uniform phase relationship in the laser energy output is found to reside in phase displacement correction of the phase distortions--such as through the use of a phase correction medium dynamically comprised of gaseous or liquid fluids.
In addition to this large chemical laser and weapons application of a phase correction arrangement, there are numerous other optical environments in which phase correction or other spatially patterned refraction needs can be met by the use of fluids disposed according to the arrangements disclosed herein. In small, gaseous, or solid state lasers, as commonly used for laboratory and mechanical purposes, phase distortions or phase aberrations are also found to occur. Similarly, in other non-laser optical apparatus, phase distortions or refraction opportunities not conveniently met by conventional materials are frequently encountered. In the large reflecting mirror art, for example, it is usually difficult and expensive to achieve extreme optical perfection, particularly in environments where practical considerations such as mirror mass and attending material sagging are considered. In each of these situations, the arrangement of the present invention offers an alternative new approach for apparatus improvement and can be attended by the opportunity for significant cost savings when compared with other phase correction arrangements.
Chemical lasers and component parts thereof are known in the patent art as is illustrated by the patents of George L. Clark, U.S. Pat. No. 4,095,193, a broad band gas laser, the patent of John W. Neal, U.S. Pat. No. 3,986,138, a gas dynamic laser nozzle with desirable temperature properties, and the patent of Arthur Dobrzelecki et al, U.S. Pat. No. 3,842,363, a chemical laser nozzle system. None of these prior patents adequately treats the correction of optical wavefront phase distortion in the laser generated optical energy.